5 Chapter 4 Nucleus

The Nucleus

• Chapter 4 introduction

What Happens To The Atom?

• Unstable isotopes undergo nuclear decay to become more stable through a spontaneous process.

• This decay results in the emission of a large amount of energy and the transformation into a different, more stable element.

Marie Curie and Radioactivity

• Marie Curie coined the term "radioactivity" to describe the phenomenon of energy emitted from certain substances.

• Key contributions include discovering new radioactive elements such as radium and polonium.

• Significant achievements:

  • PhD awarded in 1903.

  • Became a Professor of Physics at Sorbonne.

  • Received Nobel Prize in Physics (1903) and Chemistry (1911).

Radioactive Isotopes

• Out of the fewer than 300 naturally occurring isotopes, 36 are identified as radioactive.

• Isotopes with atomic numbers greater than 82 are all radioactive.

• Many artificially created isotopes are also radioactive.

• Most radiation exposure occurs from background radiation (natural sources).

The Stability of Atomic Nuclei

• Stability depends on the relative numbers of protons and neutrons within an atom.

• For stable isotopes, mass numbers are typically at least double the atomic number.

• Beta decay occurs in isotopes with an excess of neutrons, while positron emission can take place in isotopes with too few neutrons.

Nuclear Decay Processes

Types of Radiation

• Alpha Particle Emission: An alpha particle has high energy and consists of two protons and two neutrons (similar to helium-4).

• Beta Particle Emission: A beta particle is essentially an electron.

• Gamma-Ray Emission: Gamma rays represent high-energy electromagnetic radiation.

Alpha Decay

• Involves the release of an alpha particle, which is a slow-moving, high-energy particle consisting of 4 mass units and 2 protons.

• Results in the formation of a new isotope known as a daughter nuclide.

Beta Decay

• Involves the release of a beta particle (high-energy electron).

• The daughter nuclide retains the same mass number as the parent but has an atomic number that is one greater than that of the parent nuclide.

Particle Properties

• Characteristics of radiation particles:

  • Alpha (α): Charge: 0; Mass: 4 amu.

  • Beta (β): Charge: -1; Mass: negligible.

  • Gamma (γ): Charge: 0; Mass: negligible.

  • Positron: Charge: +1; Mass: negligible.

Nuclear Equations

• In nuclear equations:

  • Products are shown on the left side of the arrow and reactants on the right.

  • The sum of the mass numbers must be equal on both sides.

  • The sum of atomic numbers must also be equal.

Example: Alpha Decay Equation

• Parent Nuclide → Daughter Nuclide + α Particle

• E.g., 223_88Ra → 219_86Rn + 4_2α

  • Equation is balanced if: 223 = 219 + 4; 88 = 86 + 2.

Beta Decay Example

• For Gold-198 (β emitter):

• 198_79Au → 198_80Hg + 0_−1β

Gamma Ray Emission Example

• Example of gamma decay:

• Metastable technetium-99:

• 99m_43Tc → 99_43Tc + 0_0γ

Half-Life Concept

• The half-life of a radioactive nuclide is the time required for half of the parent nuclides to decay into daughter nuclides.

• Different radioisotopes decay at unique exponential rates.

• Examples of half-lives:

  • Uranium-238: 4.47 billion years

  • Carbon-14: 5730 years

  • Iodine-131: 8 days

Practical Examples of Half-Life

• For I-131 with a half-life of 8 days:

  • Start with 100 g:

    • After 8 days: 50 g remains.

    • After another 8 days (16 total): 25 g remains.

    • After another 8 days (24 total): 12.5 g remains.

Uses of Radioactivity

• Applications include dating archaeological sites, food irradiation, medical diagnoses, and treatment.

Carbon Dating

• Living organisms maintain a constant level of C-14, which decays post-mortem.

• Measuring remaining C-14 helps estimate the time since death, utilizing its known half-life.

Food Irradiation

• The process does not render food radioactive; it preserves food by killing harmful microbes.

• The method involves particles ionizing molecules to damage the DNA of living pathogens.

Medical Applications

• External Beam and internal isotope placement treatments for diseased tissues (e.g., iodine for thyroid therapy).

• Tracers in PET scans for diagnosing conditions like Alzheimer’s.

Average Radiation Exposure in the U.S.

• Breakdown:

  • Man-made: 18% → Medical X-rays, Nuclear medicine.

  • Natural: 82% → Radon, cosmic, terrestrial radiation.

Factors Influencing Radiation Danger

• Exposure duration, radiation type, whether internal/external, and dosage specifics.

Noteworthy Case: David Hahn

• Known as the "Nuclear Boy Scout," he attempted to build a nuclear reactor from household items, ultimately leading to his demise at age 39.

Nuclear Reactions Overview

Fission and Fusion

• Nuclear Fission: The process of splitting a large unstable nucleus, converting some mass into energy.

• Nuclear Fusion: Combines smaller nuclei into larger ones, requiring extremely high temperatures, not currently feasible for energy production.

Nuclear Fission in Power Plants

• Overview of reactor components: control rods, fuel rods, steam turbines for energy generation.

• Various countries derive a high percentage of electricity from nuclear energy.